Chapter 4 - Exponential and Logarithmic Functions - Section 4.4 Logarithmic Functions - 4.4 Assess Your Understanding - Page 322: 96

$4$

$\because y=\log_a x \text{ is equivalent to } x= a^y$ $\therefore x = \log_5 625 \text{ is equivalent to } 625=5^x$ With $625=5^4$, solve the equation above using the rule $a^m=a^n\implies m=n$ to obtain: \begin{align*} 625&=5^x\\\\ 5^4&=5^x\\\\ 4&=x \end{align*}